1. Field of the Invention
The present invention relates to a braking pressure control apparatus including two hydraulic systems for operating a hydraulically operated brake.
2. Discussion of Related Art
JP-A-5-65060 discloses a braking pressure control apparatus including (1) a brake cylinder, (2) a power-operated hydraulic pressure source operable to pressurize a working fluid to a level corresponding to an operating force acting on a manually operable brake operating member, (3) a master cylinder operable with the operating force of the brake operating member to pressurize the fluid, and (4) a solenoid-operated valve device operable between a first state for fluid communication of the brake cylinder with the power-operated hydraulic pressure source, with the brake cylinder being disconnected from the master cylinder, and a second state for fluid communication of the brake cylinder with the master cylinder, with the brake cylinder being disconnected from the power-operated hydraulic pressure source. This braking pressure control apparatus suffers from a drawback which is caused upon switching of the operating state of the solenoid-operated valve device between the first and second states, for instance, an undesirable variation of the operating state of the brake operating member.
JP-A-5-65060 also discloses an example of a braking pressure control apparatus of the type including (1) a first hydraulic system including a power-operated hydraulic pressure source operable to pressurize the working fluid and capable of controlling the pressure of the pressurized fluid, for operating a brake with the pressurized fluid delivered from the power-operated hydraulic pressure source, (2) a second hydraulic system including a master cylinder operable with an operating force acting on a manually operable brake operating member, to pressurize the working fluid, for operating the brake with the pressurized fluid delivered from the master cylinder, (3) a switching device operable to selectively establish a first operating state in which the brake is operated with the pressurized fluid delivered from the power-operated hydraulic pressure source, and a second operating state in which the brake is operated with the pressurized fluid delivered from the master cylinder, and (4) a control device for controlling the switching device such that the braking system is placed in the operating state while the first hydraulic system is normal, and in the second operating state while the first hydraulic system is abnormal.
In the braking pressure control apparatus described just above, the master cylinder provided in the first hydraulic system is adapted to pressurize the fluid on the basis of the operating force of the brake operating member, but the pressure of the fluid pressurized by the master cylinder cannot be made higher than a level corresponding to the operating force of the brake operating member. Further, the second hydraulic system is operated to operate the brake only while the first hydraulic system is abnormal.